Start with the regular formula 1 2 3 n n n 1 2 and subtract off the part you dont want 1 2 3 4 4 4 1 2 10. Heres another simple way to sum up a series of number. To make the math easier you can simplify to 7 15 105.
ROW - 4 returns 1 in B5 ROW - 4 returns 2 in B6 This formula will continue to work as long as rows are not added or deleted above the first row of data.
We will now show that a triangular number -- the sum of consecutive numbers -- is given by this algebraic formula. This average is always the middle number. To add up an entire column enter the Sum Function. The result of a formula or function appears in the cell where you entered it.